Method for obtaining dimensionally and structurally stable objects, in particular disposable containers, starting from flexible film, and object obtained by the method

ABSTRACT

A method for obtaining dimensionally and structurally stable objects, in particular disposable containers, from a flexible film rewindable on a reel, comprising the steps of preparing a flexible film rewindable on a reel, which, at least in those regions which in the obtained object are required to be substantially rigid, is associated with a structurally transformable substance inert with respect to the film and at least one passive activator therefor, forming an object from the film prepared in this manner, and during any one stage in a formation of the object, administering an energy compatible with the activator to start a structural transformation reaction of the substance and convert the regions from flexible to substantially rigid.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/EP98/02210 which has an Internationalfiling date of Apr. 15, 1998, which designated the United States ofAmerica.

This invention relates to a method for obtaining dimensionally andstructurally stable objects, in particular disposable containers,starting from flexible film, and an object obtained by the method.

Disposable containers are known obtained from sheets of resistant paper,generally plastic-coated, which are unwound from reels and subjected tosuccessive welding, folding and possibly forming processes to assume thedesired spatial shape. Their filling with liquid, granular or powderyproducts can be effected either during the container formation or afterit has been completely formed.

These known disposable containers are advantageous in terms of theirstability, stackability, shelf display, strength, product protection,ease of preservation, use and reclosability. However they are ratherheavy and costly, and are difficultly disposable as they are difficultto crumple.

Flexible disposable containers obtained from plastic film such aspolyethylene are also known, these being essentially free of thedrawbacks of rigid containers. In particular, they are of low cost,small overall size, of easy disposal, and simple, practical andadvantageous to machine-fabricate starting from reels. They are howevervirtually without dimensional stability and consequently not easy tostack, while in addition having commercial limitations as they cannot bedisplayed on shelves.

U.S. Pat. No. 3,648,834 discloses a method of forming a package from aflexible film containing a plasticizer or other constituent which iscapable of being polymerized upon being irradiated from a high energysource. After enclosing a product in such a packaging film, the thusformed package is subjected to a controlled amount of irradiation from ahigh energy source to produce cross-linking within the plasticizer orother constituent which results in the flexible packaging film becomingrigid.

An object of the invention is to eliminate the drawbacks of knowncontainers of the various types while at the same time retaining theiradvantages.

U.S. Pat. No. 3,648,834 discloses a method of forming a package from aflexible film containing a plasticizer or other constituent which iscapable of being polymerized upon being irradiated from a high energysource. After enclosing a product in such a packaging film, the thusformed package is subjected to a controlled amount of irradiation from ahigh energy source to produce cross-linking within the plasticizer orother constituent which results in the flexible packaging film becomingrigid.

An object of the invention is to eliminate the drawbacks of knowncontainers of the various types while at the same time retaining theiradvantages.

A particular object of the invention is to obtain disposable containers,and objects generally, which present dimensional stability while at thesame time being of low weight and cost and able to be crumpled to reducetheir volume after use for easy disposal.

A further object of the invention is to provide disposable containers,and objects generally, starting from flexible film which before formingthe container can be wound in a roll and hence occupy a considerablyreduced space, to be stiffened only at the moment of formation of thecontainer.

BRIEF SUMMARY OF THE INVENTION

These objects and others which will be apparent from the ensuingdescription are attained by a method for obtaining dimensionally andstructurally stable objects, in particular disposable containers, fromflexible film, rewindable on a reel, by:

preparing a flexible film rewindable on a reel, which, at least in thoseregions which in said obtained object are required to be substantiallyrigid, is associated with a structurally transformable substance inertwith respect to said film and at least one passive activator therefor,

forming an object from said film forming material prepared in thismanner, and

during any one stage in a formation of said object, administering anenergy compatible with said activator to start a structuraltransformation reaction of said substance and convert said regions fromflexible to substantially rigid.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred embodiments of this invention are further clarifiedhereinafter with reference to the accompanying drawings, on which:

FIG. 1 schematically illustrates a first embodiment of the method of theinvention,

FIG. 2 is a perspective view of a parallelepiped package obtained by themethod,

FIG. 3 illustrates a second embodiment thereof,

FIG. 4 is a perspective view of a package obtained by the method,

FIG. 5 schematically illustrates a third embodiment of the method of theinvention, and

FIG. 6 illustrates a fourth embodiment thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS

Generally according to the invention, a transformable substance such asa polyester resin and a passive activator therefor are applied to onesurface of a flexible film, for example of paper, polyethylene or othermaterial. It is important that the resin and activator are of a typewhich does not interact significantly with the film, but is able to forman agglomerate therewith. The resin and activator are applied only tothose parts which in the obtained container are required to besubstantially rigid.

After this application the applied substance is allowed to dry, afterwhich the thus treated film is rewound to await its future use by thepackager.

At the moment of packaging, the previously treated flexible film isunwound and during its unwinding is fed with energy of predeterminedpower and wavelength depending on the type of activator chosen.

While the film is being fed with energy, this acts on the activatorcausing progressive structural modification of the resin, which becomesrigid to also stiffen the film parts with which it forms theagglomerate.

If before, during or after energy administration the previously treatedfilm is subjected to traditional forming operations leading to theobtaining of a possibly filled package, the stiffening of the film partson the basis of the aforedescribed mechanism provides sufficientdimensional stability to the package obtained, notwithstanding the factthat it is constructed of an essentially flexible base material. As aresult, this package presents all the characteristics of a substantiallyrigid package while being of extremely low weight and hence cost, andable to be crumpled after use for easy disposal.

The new principle on which the present invention is based hence consistsof preparing and using a flexible film which before or after theformation of the object to be obtained is fed with energy toconsequently undergo a modification of its structure in those regionswhich in the finished object must be substantially rigid. It can be usedin various ways and be of various materials.

In the currently described embodiment the resin is applied only to thoseregions of the film to stiffened, whereas energy is administered to theentire film surface.

In a different embodiment of the method of the invention, the resin isapplied to the entire film surface whereas energy is administered onlyto those regions to be stiffened. This can be achieved using a suitablemasking screen interposed between the treated film and the energysource.

In a further embodiment of the method of the invention, the resin isapplied during the formation of the film. More particularly, the resinand its activator can be incorporated into the mass from which theflexible film is to be formed.

That film which has undergone total resin treatment, ie either byincorporating the resin into the mass to form the film or by applyingthe resin to the film already prepared, can also be firstly shaped toobtain the package, followed by total irradiation to completely stiffenit. In this case it can no longer be crumpled after use, but itpreserves all the other stated advantages, and in particular thecharacteristic of being able to defer the stiffening of the flexiblefilm until the moment in which this characteristic is required forutilization.

Various substances can be used to arrange the flexible film for local orwidespread stiffening, their properties being known to the expert.Generally these substances are photopolymerizable unsaturated resins,acrylic resins, silicone, liquid crystals, polyester resins, etc.

The energy to be administered can also be of various types, and ingeneral is chosen on the basis of the activator for the substanceapplied to the film and on the type of stiffening to be conferred on theobject. This energy can be thermal, UV, visible or infrared radiation,electronic, ionic, electrchemical, electromagnetic, nuclear, etc.

In all these described embodiments it is also possible to apply to theflexible film, after application of the stiffening resin, a further filmwhich, in contrast to the resin, is compatible with the substance to becontained in the package, in particular food substances, and/or with theoutside environment. This latter requirement is important for example inthe case of packages which can come into contact with children and musthave an absolutely toxic-free outer surface.

A different embodiment of the method of the invention is based on theprinciple of utilizing, for the controlled stiffening of all or par ofthe flexible film, the properties of certain substances which increasetheir rigidity by electrochemical transformation., which takes placefollowing contact with another substance, and occurs over a period whichis sufficiently long to enable the object to be formed before completionof the transformation.

These substance, which are available in the liquid state in the form ofsolid particles or fibres, which can also be porous, can act inaccordance with two different mechanisms, depending upon whether theypresent ablative or expanding properties.

In the first case, an ablative liquid, for example a silicone, able topass into the gaseous state on administration of energy, is applied tothe flexible film (paper) for example by spraying.

A further impermeable film is then applied to both sides of the filmtreated in this manner.

After forming the object, which is flexible, it is fed with heat, forexample in an oven. In this manner the silicone ablative process takesplace, it being converted into the gaseous state and, given itsconfinement within the micropores of the starting film and retainedthere by the two impermeable films, considerably increases its pressure,resulting in substantial stiffening and stability of the objectobtained.

The same result can be obtained by using, instead of a substance withablative properties, a structure with expanding properties (foaming),such as a polyurethane, a polypropylene, a polyethylene or an acetalsubstance.

If the starting film is of a non-porous material, the impermeable filmcan evidently be applied only to that side on which the ablative orfoaming substance has been previously applied.

A further embodiment of the method of the invention is based on theproperty, possessed by some essentially fibrous substances, ofundergoing controlled structural transformation by a shape memoryphenomenon. These substances, known as SME (Shape Memory Effect)substances, consist of microfilaments or flexible fibres which can beapplied to the film to be stiffened by adding them to the polymerizablemass from which the film is to be obtained, or by forming a mesh whichis then applied to the film to be treated.

These microfilaments, which may be metal, or flexible fibres, have ahighly flexible martensitic structure below the transformationtemperature, however above this temperature they assume an austeniticstructure, which confers rigidity on the object formed from the flexiblefilm which incorporates them.

If these microfilaments have been added to the mass from which theflexible film is later obtained, the stiffening due to their structuraltransformation extends throughout the entire object.

If however these microfilaments have been applied only to those filmregions which are to be stiffened in the formed object, the stiffeningextends only to those regions.

In further embodiment of the method of the invention, controlledstiffening of a flexible film is achieved by utilizing the propertiespossessed by certain substances of forming composites, ie of bindingtogether long or short-fibre or powder components.

According to this method, to the film to be stiffened there is applied amelamine formaldehyde which, when fed with energy, polycondenses andacts as an adhesive on the film fibres.

Alternatively a mix of melamine with fibre and powder can be extruded,so that when energized, the melamine binds the fibres together to at thesame time stiffen the object obtained. In both cases the stiffening isachieved by virtue of the structure formed by the fibres held togetherby the adhesive.

The following examples, referred to the different embodiments of themethod of the invention, clarify the invention in greater detail.

EXAMPLE 1

A mixture is prepared consisting of 60-70 vol % of an acylated urethane,of the type commercially known as Ebecryl 605, and 40-30% of amonoacrylate monomer, of the type commercially known as TPGDA1997-02125, both produced by UCB Chemical Ltd. This mixture is pouredonto a porous polyethylene film of thickness 10-100 microns to fill itspores. An activator of the type commercially known as Irgocure 651,produced by Ciba Geigy AG, is then poured in a quantity of 3-5 vol % ofthe mixture onto the film on which there is then applied a secondpolyethylene film of thickness 200 microns. A container of dimensions10×10×15 cm is constructed from this film using traditional formingtechniques.

All the corners of the container are then irradiated with four UV lampsof 80 watt/cm power, produced by Quantum S.R.L., at a rate of 20 cm/min.In this manner a dimensionally stable container with stiffened butnon-fragile corners is obtained, suitable for containing solid or liquidfoods.

EXAMPLE 2

An ablative polymer consisting of a sprayable rigid silicone material ofthe type known commercially as CPC 1050, produced by GE, is sprayed ontothe film of the previous example. The liquid quantity sprayed is chosensuch as to create an agglomerate with about 10 vol % of ablativesilicone on the polyethylene film volume. A further film is then appliedto the film treated in this manner, to form a sandwich which sealedlyretains the silicone material.

After the edges of the two films have been welded together, the sandwichfilm obtained in this manner, is used to form a container, which wasthen placed in an oven at a temperature of more then 100° C. Theablative process gave rise to the formation of gas at high pressurewhich conferred rigidity to the entire container.

EXAMPLE 3

Using the method of the previous example, instead of an ablativesilicone the polyethylene film was given an application of polyurethane,which on transformation into foam stiffened the container.

EXAMPLE 4

A microfilament mesh of 100-150 micron thickness and with squareapertures of 1 mm was prepared from a nickel-titanium alloy produced bythe Furukawa Company, and showed high flexibility in its martensiticstructure at ambient temperature. This mesh was applied to a 10-100micron thick polyethylene film, which preserved its flexibility.

A second film was then applied to this film to obtain a sandwich film ofabout 300 micron total thickness.

This was used to form a container which was then heated to above theaustenitic transform temperature of the microfilament mesh (about 75°C.) or 5 minutes in an oven. Following the austenitic transformation thecontainer became irreversibly rigid. The mesh was applied to the filmonly in those regions corresponding to the container corners, thesecorners becoming rigid to an extent four times greater than theremaining parts of the container. The width of the mesh regions wasabout 2 mm, and in the rigid regions the volume of the meshmicrofilaments did not exceed 10% of the entire volume of theagglomerate.

Some preferred container construction methods are described hereinafterwith reference to the figures.

FIG. 1 shows schematically a flexible film 2, to which a polyethyleneresin and a passive activator therefor have been applied to a measuredextent in bands 4 which are to form the corners in the package to beobtained (the example relates to a parallelepiped package).

When the package is to be formed, the previously treated flexible film 2is unwound and is subjected, gradually as it is unwound, to theadministration of thermal energy 6, which cross-links the resin withconsequent stiffening thereof and of the film with which it forms theagglomerate.

The film treated and partially stiffened in this manner islongitudinally folded-over and is joined together along its longitudinaledges to form a sort of continuous tubular element 8.

It is then welded along a transverse line and filled with a liquid,past, powdery or granular product, then welded above the filled portionand cut along the weld band 14, to be separated into a container whichis finally subjected to traditional folding and/or forming techniques toattain the desired final configuration 18.

If the package is to be made easily tearable along its contents deliveryaperture notwithstanding the substantial flexibility of the packagewalls and hence their difficulty of tearing, the polyethylene resin andits activator are also sprayed on the region scheduled for the deliveryaperture. In this manner, that part, on being stiffened by virtue of thecross-linking, is converted into a sort of blade 20 which can be easilytorn by simply pressing the surrounding wall of the package with afinger.

In a modified embodiment not shown on the drawings, after the roll offlexible film has been sprayed to a measured extent on the regions to bestiffened, the film is subjected to UV radiation at least on thepreviously sprayed regions, and is then welded along its longitudinaledges to form a tube, which is then punched to obtain pieces of shapeand dimensions corresponding to the package to be obtained. The piecesor empty packages obtained in this manner are maintained “flat” and arearranged in packs or stacks which are transferred in this state to thepackaging machine.

Here the package are filled one by one and are then closed and shaped toassume the desired three-dimensional configuration, which can be theresult either of the mere filling itself, or of filling followed byforming.

FIG. 3 schematically illustrates the method for constructing openpackage, for example trays 22. In this case the flexible film 2, sprayedwith the polyethylene resin and rewound, is fed as in the first exampleto the packaging machine, where at the moment of forming the package itis unwound and subjected to a thermoforming process in accordance withone of the traditional techcniques. In particular, this thermoformingprocess comprises a stage in which the flexible film is preheated, asubsequent stage in which it is irradiated with UV, and a final stage inwhich the preheated and irradiated film is formed, which forming cantake place in a mould by vacuum or blow-moulding or by deformation by adie and punch, and can involve a single tray or several trays at a time.

Independently of the forming technique used, on termination of thislatter a tray 22 of flexible material is obtained, with its corners andpossibly its base stiffened, and hence able to provide dimensionalstability to the tray. This can then be fed to subsequent stepsincluding filling, the application of a cover film by welding, and finalpunching of the closed tray.

FIG. 5 illustrates a further container forming method.

According to this method the film 2 is sprayed over its entire surfacewith the stiffening substance and its activator. At the moment ofpackaging the film is folded longitudinally into two parts and made topass between two half-moulds 24 comprising a plurality of mutuallyfacing cavities. During this passage the two flaps of the film 2 arethermally welded together along the edges of the cavities, and theinterior of the space bounded in this manner is filled with air ordirectly with the product to be packaged, so as in either case to causethe two film flaps to expand and to adhere to the concave wall of bothcavities. The two half-moulds 24 are partially heated, ie are heated incertain regions, to achieve a temperature higher than the minimumtemperature which causes structural transformation of the hardeningsubstance, whereas the remain regions of the two half-moulds aremaintained below this temperature. Different packages are obtaineddepending on the position of these regions.

For example, if the heated regions are the edges of the cavity of thetwo half-moulds, the package obtained is flexible with the exception ofthe weld band of the two half-packages. If instead the heated regionsare the edges of the cavity of the two half-moulds or other bandstraversing the half-packages, these will also be stiffened. Finally, ifonly these latter are heated, the package will be stiffened onlythereat.

In all the schematically illustrated methods the final package is rigidalong certain bands and flexible along all the wall bounded by saidbands. Moreover, by spraying complementary regions with lacquer, thesame techniques enable packages to be obtained having substantiallyrigid walls which can be mutually articulated at the corners so as to beable to be flattened after use and again occupy a very small space. FIG.6 shows schematically the method for obtaining a package analogous tothat of FIG. 1, but with the rigid regions and flexible regionsinverted, in accordance with the method just described.

In a further method of the invention, instead of applying the hardeningresin and its activator by spraying over the entire surface of theflexible film, a second flexible film made of a structurallytransformable substance is coupled to the film 2 and then fed withenergy only in those regions to be hardened (for example by radiation ofmeasured extent).

In a further embodiment of the method one of the two components of atwo-component polymerization system is applied to the flexible film, thesecond component being applied at the time of forming the package. Toobtain localized rigidity in this package, one of the two componentsmust be applied to only measured extent.

What is claimed is:
 1. A method for obtaining dimensionally andstructurally stable objects from a flexible film rewindable on a reel,comprising the steps of: preparing a flexible film rewindable on a reel,which, in local regions which are required to be substantially rigid, isassociated with a structurally transformable substance inert withrespect to said film and at least one passive activator therefor,forming an object from said film prepared in this manner, and during anystage in a formation of said object prior to completion of the formingof the object, administering an energy compatible with said activator tosaid local regions to only initiate a structural transformation reactionof said substance and convert said locals regions from flexible tosubstantially rigid wherein the administering of energy is selectivelydirected to said local regions to initiate the structural transformationtherein on command during said any one stage.
 2. A method as claimed inclaim 1 said substance and said activator being of a type notsignificantly interacting with said film, but able to form anagglomerate therewith.
 3. A method as claimed in claim 1 the flexiblefilm starting from a liquid prepolymer mixed with reinforcing componentsof fibrous and/or pulverulent type, to thereby obtain a matrixreinforced with reinforcing elements.
 4. A method as claimed in claim 2,characterised by using structurally transformable substances withablative properties, confined between gas-impermeable films.
 5. A methodas claimed in claim 2, characterised by using structurally transformablesubstances with expanding properties, confined between gas-impermeablefilms.
 6. A method as claimed in claim 2, characterised by applying thestructurally transformable substance and its passive activator to theflexible film after it has been prepared.
 7. A method as claimed inclaim 1, characterised by using a cross-linkable substance as thestructurally transformable substance.
 8. A method as claimed in claim 1,characterised by using a polymerizable substance as the structurallytransformable substance.
 9. A method as claimed in claim 2,characterised by applying to the flexible film a shape memory structurebased on microfilaments or flexible fibres, which is maintained at atemperature lower than the austenitic transformation temperature and,after having formed the object, is heated to a temperature higher thansaid austenitic transformation temperature, to obtain the irreversibletransformation of said structure from flexible to substantially rigid.10. A method as claimed in claim 2, characterised by using aphotopolymerizable unsaturated resin as the transformable substance. 11.A method as claimed in claim 10, characterised by using an acrylatedurethane as the structurally transformable substance.
 12. A method asclaimed in claim 10, characterised by using a monoacrylate monomer asthe structurally transformable substance.
 13. A method as claimed inclaim 10, characterised by using a mixture of an acylated urethane and amonoacrylate monomer as the structurally transformable substance.
 14. Amethod as claimed in claim 11, characterised by using ahydroxycyclohexylphenylketone as the activator for the structurallytransformable substance.
 15. A method as claimed in claim 4,characterised by using a silicone as the structurally transformablesubstance.
 16. A method as claimed in claim 5, characterised by using apolyurethane as the structurally transformable substance.
 17. A methodas claimed in claim 5, characterised by using a polypropylene as thestructurally transformable substance.
 18. A method as claimed in claim5, characterised by using a polyethylene as the structurallytransformable substance.
 19. A method as claimed in claim 5,characterised by using an acetal substance as the structurallytransformable substance.
 20. A method as claimed in claim 3,characterised in that the film is prepared form a formaldehyde melamine.21. A method as claimed in claim 1, characterised by subjecting the filmto thermal energy.
 22. A method as claimed in claim 1, characterised bysubjecting the film UV radiation.
 23. A method as claimed in claim 1,characterised by subjecting the film to IR energy.
 24. A method asclaimed in claim 1, characterised by subjecting the film to visibleenergy.
 25. A method as claimed in claim 1, characterised by subjectingthe film to ultrasonic energy.
 26. A method as claimed in claim 1,characterised by subjecting the film to electronic energy.
 27. A methodas claimed in claim 1, characterised by subjecting the film to ionicenergy.
 28. A method as claimed in claim 1, characterised by subjectingthe film to electrochemical energy.
 29. A method as claimed in claim 1,characterised by subjecting the film to electromagnetic energy.
 30. Amethod as claimed in claim 1, characterised by subjecting the film tonuclear energy.
 31. A method as claimed in claim 1, characterised byapplying the transformable substance to said flexible film to a measuredextent.
 32. A method as claimed in claim 6, characterised by applyingthe transformable substance to the entire surface of said flexible filmand administering energy to a measured extent.
 33. A method as claimedin claim 6, characterised by applying a protective further film to theflexible film after the transformable substance has been applied.
 34. Amethod as claimed in claim 6, characterised by applying thetransformable substance to the flexible film, to which energy is thenadministered subsequently by the user.
 35. A method as claimed in claim6, characterised by the forming step includes subjecting the flexiblefilm to punching after the transformable substance has been transformed,to obtain in this manner a flat empty package which is substantiallyfilled by the user.
 36. A method as claimed in claim 6, characterised byapplying the transformable substance in correspondence with the pointfrom which the package contents are to be delivered.
 37. A method asclaimed in claim 1, characterised in that after the transformablepolymer substance has been transformed, the flexible film is folded overand joined together along its longitudinal edges during the forming stepto form a tubular element, which is then welded transversely, filled,closed, separated from the tubular element and formed to assume thepredetermined final configuration of the package.
 38. A method asclaimed in claim 1, characterised in that while the film is beingtreated with the transformable substance it is made to undergo saidforming step within a mould to form therein trays with at least cornersthereof stiffened.
 39. A method as claimed in claim 6, characterised byapplying to the flexible film a second flexible film of transformablematerial and administering energy to the combination to a measuredextent in correspondence with those regions which in the obtained objectare required to be substantially rigid.
 40. A method as claimed in claim6, characterised by applying to the flexible film one of the twocomponents of a two-component polymerization or cross-linking system,and applying the second component at the time of forming the element, atleast one of the two components being applied to a measured extent.